This project investigates the pharmacological, neural, and physiological control of vocal behavior in well-characterized primate model species. Current work focuses on the expression of the isolation call, a specific vocal pattern used to re-establish contact with familiar conspecifics. New findings this year are: (1) a correlation between activity of the pituitary/adrenal system and the behavioral manifestations of social separation was found in both squirrel monkeys and rhesus macaques. In individually housed adult male squirrel monkeys, a 15-min. separation from the colony resulted in significant elevations in ACTH levels in both high- and low-rate vocalizers. Juvenile macaques separated overnight from their troop and divided into high and low ACTH subgroups showed significant differences between the subgroups in several acoustic characteristics of their isolation ("coo") vocalizations; (2) juvenile rhesus macaques with bilateral ablations of the hippocampal gyrus produce isolation coos that show fewer acoustic abnormalities relative to unoperated control subjects than do age-matched monkeys with bilateral amygdalectomies; (3) isolation coos of 4-week old rhesus macaques with prenatally corrected hydrocephalus show no difference in calling rate from unoperated age-matched controls when briefly separated, but do show differences in both the types of vocalization (more shrieks and noisy coo variants) and the structural details of their tonal coos (less pitch inflection); (4) milacemide, a synthetic anti epileptic, produces a dose-dependent decrease insolation calling in socially separated squirrel monkeys, but does not alter concomitant vigilance; (5) inhibition of the enzyme monoamine oxidase (MAO) was implicated in control of isolation call production in squirrel monkeys, since L-deprenyl and MAO-B inhibitor, produced a dose-dependent decrease in this vocalization in the absence of any behavioral signs of toxicity.